Technical Reference

Treatment Procedures.

Step-by-step waterproofing, structural repair and rehabilitation methods, grouped by the chemistry they use, each mapped to the Armstrong products that carry it out. Select a treatment to view the full procedure and product recommendations.

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Treatment · Joint, crack & leak sealing

Interior Wall & Ceiling Crack Filling

Powder crack fillers and paintable acrylic sealant before putty and paint

Applications

Hairline cracks in plasterCeiling cracksCracks at wall and ceiling anglesGaps around door and window framesSkirtings and cornicesCracks before waterproofing or painting

Procedure

Scrape off loose paint and putty along the crack and open it slightly to a V-groove, so the filler can get in fully.
Brush and blow out the dust.
Hairline and fine cracks: mix RAPIDSTRONG CRACK SEALER 85 with clean water to a smooth paste. Medium cracks and plaster repairs: use RAPIDSTRONG CRACK SEALER 75, the silica-based filler.
Force the paste into the crack with a putty knife or trowel, filling it completely with no air voids, and strike it flush.
Gaps that move, such as around door and window frames, skirtings, cornices and wall-to-ceiling angles: fill with WONDERSEAL XL from the gun, nozzle cut at 45° to the bead size, and tool it smooth at once.
Let the filler cure, sand it smooth, then finish with RAINCARE WALL PUTTY, RAINCARE CP Primer and the chosen paint. WONDERSEAL XL can be painted once it has skinned.

Important Suggestions

Find out why the wall cracked before filling it. A crack that keeps reopening, runs diagonally from a corner or carries damp needs the cause fixed first. WONDERSEAL XL is not for joints that stay wet or under water; use ROOFEXSEAL PU 212 there. Cracks on external walls take ROOFEXSEAL PU 212 or the masonry crack treatment.

Why This Treatment?

Polymer-modified powder fillers bond into a dry plaster crack and set hard enough to sand and paint over, while the acrylic sealant stays flexible where frames and junctions move, so the crack does not show through the new paint.